Disk drives store information on magnetic disks. Typically, the information is stored in concentric tracks on the disk and the tracks are divided into servo sectors that store servo information and data sectors that store customer data. A transducer (head) reads from and writes to the disk. The transducer is mounted on an actuator arm that moves the transducer radially over the disk. Accordingly, the actuator arm allows the transducer to access different tracks on the disk. The disk is rotated by a spindle motor at high speed which allows the transducer to access different data sectors on the disk.
FIG. 1 illustrates a conventional disk drive 10 that includes a magnetic storage disk 12 that is rotated by a spindle motor 14. The spindle motor 14 is mounted on a base plate 16. An actuator arm assembly 18 is also mounted on the base plate 16.
The actuator arm assembly 18 includes a transducer 20 mounted on a flexure arm 22 which is attached to an actuator arm 24 that rotates about a bearing assembly 26. The actuator arm assembly 18 also contains a voice coil motor (VCM) 28 which moves the transducer 20 relative to the disk 12. The spindle motor 14, the transducer 20 and the voice coil motor 28 are coupled to electronic circuits 30 mounted on a printed circuit board 32. The electronic circuits 30 include a read/write channel, a microprocessor-based controller and a random access memory (RAM).
The disk drive 10 typically includes multiple disks 12 and therefore multiple actuator arm assemblies 18. However, the disk drive 10 can include a single disk 12.
FIG. 2 illustrates the disk drive 10 coupled to a host computer 33 by an input/output port 34. The disk drive 10 includes a controller 36, a read/write channel 38 and interface 40. The host computer 33 uses the disk drive 10 as a data storage device. The host computer 33 delivers data access requests to the disk drive 10 via the port 34. In addition, the port 34 transfers customer data between the disk drive 10 and the host computer 33 during read and write operations.
Data is stored on the disk 12 as magnetic polarity transitions in substantially concentric tracks on its surface. Data is read from the disk 12 by positioning the transducer 20 above a desired track and sensing the magnetic polarity transitions stored within the track as the track moves below the transducer 20. Similarly, data is written to the disk 12 by positioning the transducer 20 above a desired track and delivering a write current representative of the desired data to the transducer 20.
The VCM 28 positions the transducer 20 relative to the disk 12 in response to a control signal (icontrol) generated by the controller 36. The controller 36 generates the control signal in response to an access command received from the host computer 33 via the interface 40 or in response to servo information read from the disk 12.
The channel 38 processes data that is read from or written to the disk 12. During a read operation, the channel 38 converts an analog read signal generated by the transducer 20 into digital data for the controller 36. The channel 38 also recovers timing information from the analog read signal. During a write operation, the channel 38 converts customer data received from the host computer 33 into a write current that is delivered to the transducer 20 to write the customer data to the disk 12. The channel 38 also continually processes servo information read from the disk 12 and delivers the processed servo information to the controller 36 for positioning the transducer 20.
FIG. 3 is a top view of the disk 12 illustrating a typical organization of data. The disk 12 includes concentric data storage tracks 42 for storing data. The tracks 42 are illustrated as centerlines, however the tracks 42 each occupy a finite width about a corresponding centerline. Disk 12 also includes radially-aligned servo spokes (or wedges) 44 that cross the tracks 42 and store servo information in servo sectors in the tracks. The servo information is read by the transducer 20 during read and write operations to position the transducer 20 above the desired track 42. More specifically, the servo information includes servo bursts (A, B, C and D servo bursts or the like) to generate a position error signal (PES) to position the transducer 20 relative to a track centerline during a track following operation. The disk 12 also includes customer data regions 46 between the servo spokes 44 that cross the tracks 42 and store customer data in data sectors in the tracks 42. The customer data is received from the host computer 33.
Although a small number of the tracks 42, the servo spokes 44 and the customer data regions 46 are shown for ease of illustration, the actual number of the tracks 42, the servo spokes 44 and the customer data regions 46 is considerably larger.
The disk 12 also includes a keep-out region 302 near disk's inner diameter (ID) and a keep-out region 304 near the disk's outer diameter (OD). The keep-out regions 302 and 304 are reserved for disk slip of the disk 12 based on built-in tolerance for expected disk slip. That is, no customer data is stored in the customer data regions 46 in the keep-out regions 302 and 304 because if disk slip occurs, for example due to the disk drive 10 being bumped during shipping, handling or use, the disk drive manufacturer cannot guarantee that the customer data stored in the keep-out regions 302 and 304 will be accessible. The keep-out regions 302 and 304 have sizes based on expected disk slip, and are shown with exaggerated sizes for illustrative purposes.
The disk 12 also includes a certified region 306 between the keep-out regions 302 and 304. The certified region 306 is immune to disk slip. That is, customer data is stored in the customer data regions 46 in the certified region 306 because if disk slip occurs, the disk drive manufacturer guarantees that the customer data stored in the certified region 306 will be accessible in the absence of catastrophic failure, media defects and the like. In contrast, the keep-out regions 302 and 304 are uncertified regions on the disk 12.
The disk 12 also includes a utility zone 310 located in the certified region 306. The utility zone 310 stores data for the proper operation of the disk drive 10. For example, the utility zone 310 can include a log of bad data sectors on the disk 12, diagnostic information, read channel tables, test scripts, test results, error counters, performance metrics, micro-jog tables, servo optimization tables, drive code, test code and debug information. The utility zone 310 is shown as a single track located near the ID of the disk 12. However, the utility zone 310 can include multiple tracks and can be located near the OD of the disk 12 or at any other location in the certified region 306.
During disk drive manufacturing, a servo track writer (STW) positions the transducer at radial positions over the disk so that the transducer writes the servo information on the disk with high positional accuracy. The STW is an expensive piece of capital equipment, and even a small reduction in the servo information needed to be written by the STW can result in significant time and cost savings. Furthermore, as the tracks per inch (TPI) increases, the servo write time increases since the STW makes more circumferential passes over the disk, thereby increasing the demands on the STW. Thus, unless more STWs are supplied, manufacturing times will continually increase as the TPI increases.
Disk drives have been designed to perform self-servo writing in an effort to reduce STW usage. During self-servo writing, the disk drive uses temporary servo information stored on the disk and self-servo-writing instructions stored in the utility zone to write the final servo information on the disk. Unfortunately, a discontinuity may occur in the certified region between the final servo information and the utility zone.
FIG. 4 is a flowchart 400 illustrating self-servo writing that causes a discontinuity between the final servo information and the utility zone.
The disk drive is placed in a first station that includes a STW (step 410). The STW is used to write a small band of final embedded servo information in a circumferential fashion in the certified region of the disk. The STW is also used to write temporary spiral servo information across the remainder of the certified region. More specifically, instead of using the STW to write embedded servo information in a circumferential fashion at each radius in the certified region, the STW is used to write temporary servo information in a spiral fashion by moving the transducer in a controlled manner (at a constant velocity or along a velocity profile) from the edge of the band of the embedded servo information to the edge of the certified region as the disk spins. By writing the temporary servo information in a spiral fashion, the servo write time for the remainder of the certified region is a function of the number of spirals rather than the number of tracks. However, the STW is not used to write servo information in the keep-out region.
Next, the disk drive is moved to a second station, so as to free-up the STW at the first station for other disk drives (step 420). At the second station, which includes a host connection to the disk drive, self-servo writing instructions are loaded (written) into a utility zone that is within the small band of embedded servo information in the certified region. Diagnostic information and self-test code may also be loaded into the utility zone.
Next, the disk drive is moved to a third station (step 430). The disk drive is powered-on, reads the self-servo writing instructions in the utility zone, and converts the spiral servo information into embedded servo information without further assistance from the STW. More specifically, the disk drive positions the transducer by servoing on the spiral servo information to self-servo write embedded servo information in the remainder of the certified region using the self-servo writing instructions. However, the self-servo writing does not write servo information in the keep-out region. FIG. 5A illustrates a discontinuity 510 between the embedded servo information in the utility zone written using the STW and the embedded servo information in the certified region adjacent to the utility zone written by the self-servo writing. The discontinuity 510 extends substantially about a radius of the disk surface. The discontinuity 510 reflects that the embedded servo information in the utility zone is radially incoherent with the embedded servo information outside the utility zone. The discontinuity 510 arises (or is likely to exist) since the embedded servo information in the utility zone is written at a significantly earlier time than the embedded servo information outside the utility zone. Thus, the discontinuity 510 may be due to changes in environmental conditions between the two servo writing operations. For example, thermal changes may occur between the two servo writing operations. In addition, handling the disk drive (such as moving it from station-to-station) may cause alignment changes (such as spindle tilt).
Because the utility zone is accessed during normal operation of the disk drive, the transducer must cross over the discontinuity during seek operations that move the transducer into or out of the utility zone. As a result, special drive code is required to accommodate the discontinuity. Furthermore, accessing the special drive code may delay the seek operations, thereby degrading the performance of the disk drive.
Accordingly, there is a need for self-servo writing without creating a discontinuity between the final servo information and the utility zone.